High pressure reciprocating pumps are commonly used for high pressure oilfield applications, such as, for example, hydraulic fracturing. When such pumps are used for hydraulic fracturing, a reciprocating plunger causes the fracturing fluid to flow into and out of a fluid chamber which is formed in a “fluid end” body of the pump. As the plunger moves away from the fluid chamber, the fracturing fluid is drawn through an inlet valve into the fluid chamber. Then, when the plunger changes direction and moves toward the fluid chamber, the fracturing fluid is discharged from the pump through an outlet valve.
A high pressure reciprocating pump assembly 10 of the type heretofore used in the art is illustrated in FIGS. 1A and 1B. The pump assembly 10 can be installed in fixed position or can be mounted on a trailer or skid for moving from site to site on land or offshore. The pump assembly 10 comprises a power end 12 and a fluid end body 20. The fluid end body 20 is coupled with the power end 12 by a set of stay rods 16.
The fluid end body 20 of the pump assembly 10 can have one or a plurality of internal fluid chambers 22. For each of the internal fluid chambers 22, the fluid end body 20 comprises: a suction bore 26 through which a fluid is drawn from a suction manifold 28 into the fluid chamber 22; a suction valve 24 within the suction bore 26; a discharge access bore 32; a discharge valve 30 accessible via the discharge access bore 32; a plunger bore (cylinder) 34 in communication with the fluid chamber 22; a plunger 36 which is slidably received in the plunger bore 34 for reciprocating movement toward and away from the fluid chamber 22; and an access bore 38 which provides access to the plunger bore 34 and to the suction bore 26.
The suction bore 26 extends inwardly from a first face 25 of the fluid end body 20 to the internal fluid chamber 22. The discharge access bore 32 extends inwardly from a second face 31 of the fluid end body 20 to the internal fluid chamber 22. The plunger bore 34 extends inwardly from a third face 31 of the fluid end body 20 to the internal fluid chamber 22. The access bore 38 extends inwardly from a fourth face 37 of the fluid end body 20 to the internal fluid chamber 22.
The power end 12 of the pump assembly 10 comprises a drive assembly 13 which is contained within a power end housing 15. The drive assembly 13 comprises: a crankshaft 50; a bull gear 52 which rotates the crankshaft 50; and a pinion gear 54 which engages and drives the bull gear 52. An engine or motor (not shown) is connected or linked to the pinion gear 54 for directly or indirectly driving the pinion gear 54 during operation.
In the pump assembly 10 shown in FIG. 1, a connecting rod 56 mechanically connects the crankshaft 50 of the power end 12 to a cross head 58 via a wrist pin 60. The crosshead 58 is mounted for reciprocating linear movement within a stationary crosshead housing 62. A pony rod 64 is connected between the crosshead 58 and the plunger 36 for driving the reciprocating movement of the plunger 36 within the plunger bore (cylinder) 34 of the fluid end body 20. It will be understood, however, that the plunger 36 can alternatively be directly coupled with the crosshead 58 such that the pony rod 64 would be eliminated.
As will also be understood by those in the art, the fluid end 20 of the pump assembly 10 can have a single reciprocating plunger 36 or can have multiple plungers 36 which operate in a corresponding number of cylinders 34, depending upon the fluid flow capacity required. The reciprocating plunger pumps most commonly used for hydraulic fracturing are 3 cylinder (triplex) pumps and 5 cylinder (quintuplex) pumps.
As illustrated in FIG. 1A, each plunger 36 used in the pump assembly 10 extends through a plunger bore (cylinder) 34 of the fluid end body 20 so as to interface with a corresponding internal fluid chamber 22. As the plunger 36 moves longitudinally away from the chamber 22, the pressure inside the fluid chamber 22 decreases, thus creating a differential pressure across the suction valve 24. A biasing member 68 (e.g., a spring) located between the suction valve 24 and a valve stop 70 maintains a predetermined closing force on the suction valve 24, thereby maintaining the suction valve 24 in a closed position until the differential pressure across the suction valve 24 reaches a point which is sufficient to overcome the force generated by the biasing member 68.
When this point is reached, the suction valve 24 opens to allow the fluid to enter the fluid chamber 22 from the suction manifold 28. The fluid then continues to be drawn into the fluid chamber 22 until the pressure differential between the fluid inside the chamber 22 and the fluid pressure inside the suction manifold 28 is reduced to a point at which the suction valve 24 automatically returns to its closed position (via, e.g., the biasing mechanism 68 of the suction valve 24 and/or the pressure within the chamber 22).
As the plunger 36 then changes direction and moves longitudinally toward the fluid chamber 22, the fluid pressure inside the chamber 22 increases to produce a pressure differential across the discharge valve 30 which acts against the closing force of a biasing spring 74 to open the discharge valve 30 so that the fluid is discharged from the fluid chamber 22 of the fluid end body 20 via discharge bore 66 and a discharge port 65.
The pump assembly 10 also includes: a pressure containing closure 80 for each plunger bore 34 of the fluid end body 20; a pressure containing closure 84 for each discharge access bore 32 of the fluid end body 20; a pressure containing closure 86 for each access bore 38 of the fluid end body 20; and a pressure closure 89 for the side bore 66 of the discharge port 65. FIG. 1B also shows pressure gage connections 91 and 93 installed through the closures 84 of two of the discharge access bores 32.
Heretofore, the pressure containing closures used in the industry in the fluid end bodies of high pressure reciprocating pumps have been either (a) threaded closures of the type illustrated in FIG. 2 or (b) flanged closures with threaded studs as illustrated in FIG. 3.
When using a prior art threaded closure 90 of the type illustrated in FIG. 2 (also referred to as a threaded retainer), the threaded closure 90 will be received within the outer end of the bore 34, 32, 38 or 66 of the fluid end body 20 for closing the outer end of the bore and for holding an internal seal member 92 (e.g., a cover 97 with a surrounding O-ring or other seal element 99) in contact with a radial retaining shoulder 94 formed within the bore 34, 32, 38 or 66. The prior art threaded closure 90 includes threads 96 which are formed around the cylindrical exterior of the closure 90 and which mate with, and are received by, threads 98 which must be formed in the fluid end body 20 around the cylindrical interior wall 100 of the bore 34, 32, 38 or 66.
It is also known in the art that the threaded closure (retainer) 90 and the cover 97 can alternatively be formed together as a single element.
When using a prior art flanged pressure containing closer 102 of the type illustrated in FIG. 3 (also referred to as a flanged retainer), a cylindrical body portion 104 of the flanged closure 102 will be received within the outer end of the bore 34, 32, 38 or 66 of the fluid end body 20 for closing the outer end of the bore and for holding the internal seal member 92 (e.g., a cover 107 with an O-ring or other surrounding seal element 111) in contact with the radial retaining shoulder 94 formed within the bore 34, 32, 38 or 66. In addition, the flanged closure 102 also comprises a radial flange 106 which is provided at the outer end of the cylindrical body portion 104 and which will extend over the exterior surface 105 of the fluid end body 20 around the outer end of the bore 34, 32, 38 or 66. The flanged closure 102 is retained in closed position on the fluid end body 20 by at least 2 threaded studs 108 which extend through bores 112 provided in the radial flange 106. As shown in FIG. 3, each of the stud connections requires that a corresponding threaded bore 110 for threadedly receiving a distal portion 109 of the stud 108 must be formed in the fluid end body 20 adjacent to the outer end of the bore 34, 32, 38 or 66.
It is also know in the art that the flanged closure 102 and the cover 107 can alternatively be formed together as a single element.
Thus, the prior art threaded closure 90 and the prior art flanged closure (retainer) 102 which uses threaded studs 108 each require that attachment threads 98 or 110 for receiving the threaded closure 90 or the threaded studs 108 must be formed in the fluid end body 20 of the pump assembly 10. The threads 98 or 110 formed in the fluid end body 20 are difficult and costly to machine and costly or impossible to repair if the threads 98 or 110 are damaged during machining or assembly. In addition, the prior art threaded closures are subject to thread fatigue failures due to the highly fluctuating pressure conditions produced in high pressure reciprocating pumps.
The cost of repairing or replacing a damaged fluid end body for a 3 cylinder (triplex) or 5 cylinder (quintuplex) pump will typically be at least $1,000.00 and can be as much as $100,000.00 or more.
Also, to sufficiently tighten the prior art threaded closures 90, the closures must be hammered during assembly. This presents not only a further risk of damaging the fluid end body 20 of the reciprocating pump, but also poses a risk of injury to the workman if the correct procedure is not carefully followed.
Consequently, a need exists for improved fluid end closures for high pressure reciprocating pumps which (a) do not require the machining of attachment threads in the fluid end body, (b) do not require hammering during assembly, and (c) are less expensive to produce and install.